A wide variety of spray application devices for applying liquids such as paint, varnish, cleaning solvents, or other liquid materials to a surface are known. Typically, such spray applicator devices include a supply vessel that contains a volume of the liquid to be applied to the surface. The liquid is transferred from the supply vessel to a spray gun that atomizes the liquid and projects the atomized liquid towards the surface. In one example of a spray applicator device, the supply vessel is positioned above the spray gun so that the liquid is transferred to the spray gun by a gravity-feed system. In another example of an applicator device, the supply vessel may be positioned below the spray gun and internally pressurized to transfer the liquid upwardly into the gun. In still other examples, the vessel may be positioned remotely relative to the gun so that the liquid is transferred from the vessel to the spray gun through a flexible hose.
In all of these spray applicator devices, determining the volume of the liquid remaining in the supply vessel as the application of the liquid proceeds constitutes a significant problem. If the liquid volume in the supply vessel is reduced to a low value, the gun may be supplied with liquid only intermittently, so that the gun emits the atomized liquid on an interrupted basis. As a consequence, the spray applicator device fails to apply the liquid uniformly to the surface. In particular, when the spray applicator device is used to apply a paint material to a surface, surface imperfections in the paint finish may result when non-atomized paint is projected, or “sputtered” onto the surface, thus necessitating time consuming surface rework and re-painting. Since supply vessels commonly used with spray guns are comprised of materials that are substantially non-transparent, a visual indication of the liquid level in the supply vessel is not generally possible.
Accordingly, there is a need in the art for a level-sensing device for spray applicators to provide a user of the spray applicator with an audible or visual indication when the volume of liquid in the supply vessel has been reduced to a predetermined level.